In order to circulate blood, hearts beat or contract regularly. The rate (frequency) of the heart's contraction changes to keep-up with increased demand for oxygen for exercise. The harder you push, the faster your heart will beat. As I will show elsewhere, your heart rate is a VERY useful thing to know when exercising and it is extremely easy to measure.
When the heart contracts during the systolic phase of its "beat" it forces blood into the arteries and causes a large pressure wave to "thump" through every artery in the body in the same way say, jumping on a garden hose causes a pulse of water pressure. You can feel the pressure from a heartbeat in every large artery in the body. There are two places where this is most easily felt: the radial artery in the wrist and the carotid artery in the neck.
To feel your wrist pulse take one hand and place it on the wrist of the other arm as shown in the picture.
Once you have your finger over the area shown, press down lightly and feel for a soft and rythmic thumping. That is the pressure pulse caused by each beat of your heart. Each thump represents one beat.
Heart rate is just that, a RATE, and it's always measured in beats per minute. So to measure your heart rate from your wrist, you count-up the number of pulses that occur in one minute. It's simple. The only problem is that a minute is a long time to wait when you're exercising so most people count beats in 15 seconds. Since 15 seconds is exactly one-forth of a minute, all you have to do to get your beats per minute is multiply your beats per-15 seconds by four.
How to Measure Your Heart Rate: (Old Version)
As noted earlier, heart rate is simply the number of times the heart beats in one minute. But how can you tell when your heart beats? Easy…. You feel for an arterial "pulse". Each time the heart beats, it squeezes blood out of the heart and into the circulation. This pushes the blood along and also creates a pressure wave or pulse that we you can feel with your fingertips. And you can feel it anywhere there is a large or medium-sized artery: the neck, the wrist, the ankle, etc. Generally the two best places to feel your pulse are the neck or the wrist. The trick is feeling in exactly the right place. Fortunately, the right place is easy to find as shown in the pictures below.
Once you have found the pulse you can count it. The time-consuming way to measure your heart rate is to count the number of pulses in a whole minute by looking at your watch while you count each pulse. When a minute has passed, voila!, the number of pulses you just counted is your heart rate. But, as I said, that takes a whole minute. A quicker way to check your heart rate is to count the pulses in fifteen seconds or a quarter of a minute. All you need to do then is multiply the number of pulses you counted over that fifteen seconds by four (fifteen seconds is a fourth of a minute) to get you heart rate.There IS an even easier way to check heart rate: buy a heart rate monitor. Such devices are now sold in most sporting goods stores and they work by essentially "feeling" your pulse for you. The only downside to a heart rate monitor is that they cost money, but most sell for less than $50, some less than $20